1. Technical Field
The present invention relates to a light source device and a projector including the light source device.
2. Related Art
A projector which forms a light image by modulating light emitted from a light source device and projects the formed light image on a screen or the like is known. The light source device contained in the projector includes an arc tube and a reflector for reflecting light emitted from the arc tube. The arc tube has a light emission portion containing a pair of electrodes, and sealing portions extending from both sides of the light emission portion. A type of the light source device included in the projector has a sub mirror on the arc tube to use light emitted from the arc tube with high efficiency. According to this type of light source device, heat generated by light emission needs to be cooled so as to adjust the temperature of the arc tube to an appropriate temperature.
FIG. 9 is a cross-sectional view illustrating the side of a light source unit including a light source device in related art. As described above, a light source device 69 in the related art includes an arc tube having a light emission portion 81 and sealing portions 82 and 83, a reflector 70, a sub mirror 90 and other parts. A light source unit 8 includes the light source device 69, a concave lens 11 for collimating light emitted from the light source device 69, a housing 9 for accommodating the light source device 69 and the concave lens 11, and other components. The housing 9 has an air intake port 9a through which cooling air W is introduced, and an air discharge port 9b through which the cooling air W flowing within the housing 9 is discharged from the housing 9. Furthermore, a cooling fan 511 for delivering the cooling air W, a duct 521 for guiding the cooling air W toward the air intake port 9a, a louver 531 for controlling the flowing direction of the cooling air W to be introduced from the air intake port 9a into the housing 9, and others are provided outside the light source unit 8 (inside the projector including the light source unit 8). Heat generated by light emission from the arc tube 80 is cooled by the light source unit 8, the cooling fan 511 and others.
According to a technology disclosed in JP-A-2008-216727, a rectifying portion is disposed around the sealing portions of the light source device described above at a position out of the effective optical path particularly for preventing excessive increase in the temperature of the upper area of the arc tube by cooling the light emission portion with high efficiency.
However, when cooling air is supplied to the light source unit 8 in the related art to cool the heat generated by the arc tube 80 of the light source device 69, the cooling air W tends to flow along the inner surface of the reflector 70 (a reflection layer 73) as indicated by arrows in FIG. 9. In this case, the speed of airflow between the light emission portion 81 and the reflector 70 (the reflection layer 73) in the direction of an illumination axis L increases. As a result, the flow of the introduced cooling air W to an area A in the upper region of the light emission portion 81 as an area having a high temperature due to heat convection is limited, and thus the area A cannot be efficiently cooled. When the airflow amount or the airflow speed of the cooling fan 511 is raised so as to adjust the temperature of the area A in the upper region of the light emission portion 81 having the high temperature to an appropriate temperature, an area B on the reflector 70 side of the light emission portion 81 is excessively cooled. In this case, the temperature difference in the temperature distribution in the direction of the illumination axis L increases. Particularly, in case of the light source device including the sub mirror 90 and thus having a relatively larger distance between the light emission portion 81 and the reflector 70 in the direction of the illumination axis L than the distance of a light source device not including the sub mirror 90, the temperature difference becomes more remarkable.
When the excessively cooled condition continues in the area B, the inner wall in the area B of the light emission portion 81 is blackened. When the air supply is decreased so as to prevent excessive cooling in the area B, the temperature of the area A is raised to a high temperature. As a result, the inner wall in the area A of the light emission portion 81 is easily whitened. The blackening refers to a phenomenon where evaporated atoms of a base material constituting an electrode (such as tungsten atoms) do not return to the electrode but adhere to the inner wall of the light emission portion 81 when a halogen cycle of the base material is not normally performed due to the low temperature. The whitening herein refers to a phenomenon which whitens a base material constituting the light emission portion 81 at the time of recrystallization of the base material caused by the high temperature. When the whitening or blackening is produced, the area corresponding to the whitening or blackening loses transparency in either of the cases and lowers the amount of light emitted from the light source device 69.
Therefore, such a light source device and a projector have been demanded which can efficiently cool generated heat, properly control the temperatures of the upper area of the light emission portion and the reflector side of the light emission portion, reduce the temperature difference on the light emission portion, and obtain uniform temperature distribution in the direction of the illumination axis.